The present invention concerns a measurement device for the mounting of corrective glasses on a spectacle frame, and especially corrective glasses having progressively variable focal power.
The device according to the present invention allows, on the one hand, to measure the distance separating the center of each pupil of a patient's eye from the point that is situated on the lower, internal edge of the corresponding circle of the frame and that is vertically the furthest from the center of the pupil and, on the other hand, to verify the compatibility of the frame with the prescribed corrective glasses. A device adapted to fulfill this function has already been proposed, especially in French Pat. No. 77 07641, in the name of the applicant (French publication No. 2,384,232).
However, the device described in this patent is destined to be placed in the rim groove of one of the circles of a spectacle frame and cannot be used in combination with a clip frame or a frame of which the upper or lower part of the circles comprises by a flexible thread, for example, a nylon thread.
Furthermore, this device is difficult to use with frames, of which the lowest parts of the circles are very eccentric and situated on the side of the temples of the spectacle wearer.
Other measurement devices for use in combination with any type of frame exist, such as described in U.S. Pat. No. 1,675,407. These devices comprise by a graduated scale disposed on a transparent plate. It has been shown from experience that these devices are not sufficiently precise, since it is difficult to carry out an exact reading while checking that the patient indeed observes the distant point or object that has been designated; and these devices conception and the manner of utilization resluting therefrom, are the give rise to measurement errors due essentially to a lack of parallax.
One of the aims of the present invention is to overcome the disadvantages of such prior art measurement devices and to enable the practitioner to carry out a rapid measurement that is both objective and subjective and, consequently, to obtain high precision with respect to the real needs of a spectacle user.
Furthermore, the device according to the invention enables measurement of the horizontal distance separating the center of each pupil from the internal edge of the corresponding circle situated on the temporal side and the furthest from the pupil.